MD Settings: Eliminate remaining references to paper-dropdown-menu-light

chrome/browser/resources/settings/settings_shared_css.html

 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="/settings_vars_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style include="cr-shared-style">
       /* Included here so we don't have to include "iron-positioning" in every
        * stylesheet. See crbug.com/498405. */
       [hidden] {
@@ skipping 45 matching lines @@
       paper-button[toggles][active] {
         background-color: var(--paper-grey-300);
       }
 
       paper-toggle-button {
         @apply(--settings-actionable);
         height: var(--settings-row-min-height);
         width: 31px;
       }
 
-      paper-dropdown-menu-light {
-        --iron-icon-fill-color: var(--paper-grey-600);
-        --paper-font-subhead: {
-          font-size: inherit;
-        };
-        --paper-dropdown-menu-input: {
-          border-bottom-color: var(--paper-grey-300);
-        };
-        /* Offsets the input's border-bottom. */
-        top: 1px;
-      }
-
-      iron-dropdown .dropdown-content,
-      paper-dropdown-menu-light paper-listbox {
+      iron-dropdown .dropdown-content {
         min-width: 128px;
         padding: 8px 0;
       }
 
       .dropdown-item {
         align-items: center;
         background: none;
         border: none;
         box-sizing: border-box;
         color: var(--paper-grey-800);
         display: flex;
         font: inherit;
         min-height: 32px;
         padding: 0 24px;
         text-align: start;
         width: 100%;
       }
 
-      paper-dropdown-menu-light .dropdown-item.iron-selected {
-        font-weight: bold;
-      }
-
-      iron-dropdown .dropdown-item:focus,
-      paper-dropdown-menu-light .dropdown-item:focus {
+      iron-dropdown .dropdown-item:focus {
         @apply(--cr-selectable-focus);
       }
 
       iron-dropdown .dropdown-content {
         background-color: white;
         box-shadow: 0 2px 6px var(--paper-grey-500);
       }
 
       .dropdown-item:not([disabled]),
       iron-dropdown .dropdown-content paper-item {
@@ skipping 314 matching lines @@
       /* Turns the arrow direction downwards, when the bubble is placed above
        * the anchor element */
       .search-bubble-innards.above::after {
         -webkit-transform: rotate(-135deg);
         bottom: -5px;
         top: auto;
       }
     </style>
   </template>
 </dom-module>